How to get the numeric index/position to face in parent shape (OpenCascade)

Question

I'm using OpenCascade to get edge vertices in a triangulation. For this I use the help of an edge-to-face map with edges as keys to the matching faces. However, I would also like to get the numeric index of the face in the parent shape (the face number if I for example use TopoDS::Face(face_map(int face_number))).

TopTools_IndexedMapOfShape edges;
TopExp::MapShapes (parent_shape, TopAbs_EDGE, edges);

TopTools_IndexedDataMapOfShapeListOfShape edge2FaceMap;
TopExp::MapShapesAndAncestors(shape, TopAbs_EDGE, TopAbs_FACE, edge2FaceMap);

for (int iedge = 1; iedge <= edges.Extent(); iedge++) {

  const TopoDS_Edge& edge = TopoDS::Edge(edges(iedge));
  const TopoDS_Face& face = TopoDS::Face(edge2FaceMap.FindFromKey(edge).First());

  // Get vertices...
}

I can loop over all faces and match the mapped face, but this seems quite inefficient.

TopTools_IndexedMapOfShape face_map;
TopExp::MapShapes(shape, TopAbs_FACE, face_map);

for (v = 1; face_number <= face_map.Extent(); face_number++) {
  if( face.IsSame(face_map(face_number)) ) {
    // Found face index.
  }
}

Is there a better or alternative approach to achieve this?